1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus for illuminating a plurality of tracks on an information recording medium and recording and/or reproducing information on or from the plurality of tracks simultaneously.
2. Description of the Related Art
With the development of information industries, an optical information recording/reproducing apparatus has won popularity as a large-capacity storage in recent years. The optical information recording/reproducing apparatus includes an optical card apparatus in which an optical card is used as a recording medium to record and/or reproduce information. The optical card has a storage capacity that is several thousands times or ten thousand times larger than a magnetic card. Although the optical card as well as the optical disk cannot be rewritten, the large storage capacity of one to two megabytes the optical card has offers a large range of applications, such as a bankbook, a portable map, and a prepaid card for shopping. Moreover, the feature that the optical card cannot be rewritten proposes the usage as a personal health care card and other applications in which data must not be modified. Various optical information recording/reproducing apparatuses have been proposed to record or reproduce information using an optical disk as a recording medium in the past.
In optical information recording/reproducing apparatuses using optical cards, an optical card is reciprocated to record or reproduce information. Therefore, the reproduction speed is not very high.
In an effort to speed up reproduction, multiple tracks are read simultaneously during reproduction (hereafter, Multi-track Read).
A system of an optical information recording/reproducing apparatus based on Multi-track Read will be described as related art in conjunction with the drawings.
FIG. 7 shows an optical card. An optical card 25 is made up of ID fields 43a and 43b in which track address information has been recorded, and a data recording field 44 for recording/ reproducing data.
FIG. 8 outlines the relationship between a pattern on an optical card and a read/track detector 34. As shown in FIG. 8, a light beam 40 is emitted on the card. Guide tracks 37, tracks 38, and data pits 39 are imaged on the read/track detector 34 via an objective 28.
FIG. 9 shows the read/track detector 34 in more detail. In FIG. 9, guide tracks 37a, tracks 38a, and data pits 39a correspond to the guide tracks 37, tracks 38, and data pits 39, respectively, in FIG. 7.
Symbols 41a to 41f denote read detectors D1 to D6 for reading multiple tracks (herein, six tracks) simultaneously. By calculating the difference between data read by track detectors 42a and 42b, a track error signal can be generated. Thereby, a tracking servo is activated to position the read detectors D1 to D6 on tracks 38a all the time.
A light beam 40 is split by a beam splitter (not shown) disposed on an optical path between the objective 28 and the read/track detector. The position of the light beam 40 on a focus detector (not shown) is detected to generate a focus error signal. With the focus error signal, a focusing servo is activated to focus the light beam 40.
FIG. 10 is a block diagram of circuits for coding the outputs of the read detectors D1 (41a) to D6 (41f) in binary form. The outputs of the read detectors D1 (41a) to D6 (41f) are converted in current and voltage by I-V converters 45a to 45f, then compared with a fixed comparison value SH by binary circuits 46a to 46f. This provides binary-coded signals 1 (47a) to 6 (47f). Then, data is read.
However, when multiple tracks on a card are illuminated to reproduce the information of the multiple tracks, as shown in FIG. 11, the quantities of light in the skirts of the light beam 40 for reproduction become smaller to cause an uneven quantity of light. This decreases a marginal level required for coding in binary form when data of tracks coming in the skirts of an illumination light are reproduced. At the worst, reproduction is disabled.
In other words, FIG. 12 shows the waves of signals to be coded in binary form. The outputs of read detectors D3 (41c) and D4 (41d) (3 and 4 in FIG. 12) lying in the center of a light beam 40 are coded in binary form correctly. The outputs of read detectors D1 (41a) and D6 (41f) (1 and 6 in FIG. 12) have smaller waves because of an uneven quantity of light, and therefore cannot be coded in binary form correctly using the same comparison value SH.